Shows a modal message box with the specified message and title.
Message - The dialog message.
Title - The dialog title.
Positive - The text to show for the "positive" button. Pass "" if you don't want to show the button.
Cancel - The text to show for the "cancel" button. Pass "" if you don't want to show the button.
Negative - The text to show for the "negative" button. Pass "" if you don't want to show the button.
Icon - A bitmap that will be drawn near the title. Pass Null if you don't want to show an icon.